1. Field of the Disclosure
The disclosure is related to a method for recovery of lost and/or corrupted data.
2. Discussion of the Background Art
Data is transmitted from a transmitter device to a receiver device over a transmission channel. This can be done for example in the context of using satellite systems for broadcast of information to users. A broadcasting of data from a source via a satellite to several users, which all receive the same content, is organized in data packets, e.g. IP datagrams. Due to the transmission channel conditions the users will experience different bit error rates and thus packet error rates (PER). Due to the packet error rates a part of the received packets for each user will be erroneous. The packets, which are received erroneous by different users, are not necessarily the same. This scenario is illustrated in FIG. 1. In the case that a return channel or return link is not available retransmission requests cannot be sent.
A possible countermeasure is the use of so called packet loss recovery codes. The main concept of a packet loss recovery code is presented in FIG. 2. First a set of k packets to be transmitted is encoded through a packet level encoder, which produces m parity packets. The set of m+k packets is then processed by the physical layer transmitter chain. This means that the packets, both information and parity packets, are encoded via a physical layer forward error correction code, then they are modulated and transmitted. The channel impairments may cause physical layer frame errors and consequently the physical layer forward error correction code may fail in decoding a packet. This can be checked via an error detection code (e.g. CRC). Therefore from the upper layer perspective on the receiver side the packets can arrive either correctly or they are lost. The packet level decoder can then recover the missing packets by exploiting the parity packets. It can be proved that ideally it is sufficient to receive correctly k-packets out of the m+k ones to recover the full set of m+k-packets. Thus loss rates up to m:(m+k) can be tolerated.
The above mentioned method has been described taking into consideration a point to point link. When it is applied to a broadcasting scenario the number of redundant packets (parity packets) to be used has to be adapted to the user experiencing the highest packet loss rate. In other words the system designer has to derive a model of the loss rate distribution among the users and must decide about a coding rate that is able to satisfy all or at least most of them. This may lead to a loss of efficiency, since other users usually will experience lower packet loss rates.
A possible alternative to lowering too much the coding rate resides in enlarging the number of packets, on which packet level coding is applied. Usually in wireless communication systems the packet loss events are usually correlated in time, meaning that they appear in bursts. Enlarging the window, on which coding is applied, permits to average the channel behavior over a larger time. This usually leads to a reduction of the peak loss rates and thus permits to use a more efficient code scheme, namely one with less parity packets. The drawback is that latency will increase, which may not be acceptable for services with specific time requirements, for example when voice or multimedia content has to be delivered.
It is an object of the present disclosure to provide for a method for recovery of lost and/or corrupted data, which offers an improved efficiency.